The present invention relates generally to a magnetoresistive (MR) sensor. More specifically, the present invention relates to an MR read sensor and a method of fabricating the MR sensor that combines a hard-biasing material with a cubic-titanium-tungsten underlayer, which improves the stability of the MR sensor.
Magnetoresistive (MR) sensors utilize an MR element to read magnetically encoded information from a magnetic medium, such as a disc, by detecting magnetic flux stored on the magnetic medium. An MR sensor must be properly biased in both the longitudinal and transverse directions to maintain the sensor in its optimal operating range so that it can properly detect the magnetic flux. This dual biasing is established through various combinations of magnetic exchange coupling or magnetostatic coupling of various layers within the MR sensor.
The three critical layers of an MR sensor are the MR element layer, a spacer material layer, and a soft adjacent layer (SAL). The MR element has magnetoresistive properties and low resistivity and generates an output voltage when a sense current flows through the layer. The output voltage varies in the presence of magnetic flux from a storage medium. The SAL is a magnetic bias layer with high resistivity. The SAL provides transverse biasing of the magnetization of the MR element. The spacer material has non-magnetic properties and high resistivity and functions as a spacer between the MR element and SAL. The spacer material helps break the exchange coupling between the MR element and the SAL, which allows the magnetic layers to act as two distinct layers, rather than one strongly coupled layer. Hard-biasing material is placed on each end of the MR sensor to establish longitudinal biasing of the MR element and form two passive regions of the sensor. The space between the passive regions maintains the transverse biasing and is referred to as the active region of the sensor.
MR and SAL elements can "fracture" into multiple magnetic domains when they are exposed to an external magnetic field. To maximize the stability and output of the MR sensor, it is desirable to maintain the MR and SAL elements in a single domain state. Three methods for maintaining the MR and SAL elements in a single domain state are magnetostatic coupling, ferromagnetic exchange coupling, and antiferromagnetic exchange coupling. Magnetostatic coupling is accomplished by positioning a hard-biasing material or permanent magnet adjacent to the MR element. This type of stabilization scheme is known as an abutted junction scheme. Exchange coupling is accomplished by depositing a ferromagnetic or antiferromagnetic layer adjacent to the MR layer so that one of the magnetic lattices of the deposited magnetic layer couples with the magnetic lattice of the MR element layer to preserve the single domain state of the sensor. This type of stabilization is referred to as an overlaid structure.
In existing MR sensors, alignment tolerances between various thin film layers and MR sensor mask features are critical. The alignment tolerances in many prior art MR sensor designs greatly increases the complexity of processing because critical geometries frequently require additional and/or more difficult processing steps. Additional processing steps increase the variance and contamination of the various thin film layers.
In the passive region of the sensor, for example, the hard-biasing material is inherently sensitive to the crystal texture of the underlayer and to the cleanness and/or roughness of the film interface. One prior art MR structure deposits the MR element first and then deposits the hard-biasing material on top of the MR element in the passive regions of the sensor. The MR element must be sputter-etched to remove a portion of the MR element in order to establish a proper underlayer for the hard-biasing material. This process is expensive and can be hard to control. A second MR structure deposits a separate material, such as Sendust, as an underlayer for the hard-biasing material. The hard-biasing material, however, is still very sensitive to the film interface. This sensitivity affects the stability of the hard-biasing material and in turn the biasing of the MR element.
A third MR structure deposits Chromium as the underlayer for the hard-biasing material. Chromium, however, must be deposited at elevated substrate temperatures to achieve the proper texture to bond with the hard-biasing material. Depositing Chromium at elevated sputtering temperatures has severe limitations in a volume production environment.
Therefore, there is a continuing need for an underlayer that can both improve the stability of the hard-biasing material and be deposited at normal sputtering temperatures.